Measurement of urinary proteins is not only useful for the diagnosis of diseases and pathological conditions of the kidney and urinary system but also of the circulatory system and other organs in the entire body. It is known, however, that the measurement of urinary proteins is affected by the variations in the pH, inorganic salts and other low molecular weight components in the urine. The pH, inorganic salts, and other low molecular weight components vary due to the pathological conditions. In the prior art neat urine is extensively diluted with a buffer solution for the measurement of urinary proteins, in order to reduce the effect of the urine composition. Some of the urinary proteins drawing recent attention are present in urine in low concentration and are hardly detectable if they are extensively diluted as in the prior art.
Podocalyxin, a functional molecule expressed in the glomerulus epithelial cells, plays an important role in keeping the function and morphology of the glomerulus. Patent Document 1 discloses a method for measuring human podocalyxin in a sample, comprising: reacting the sample with first anti-human podocalyxin antibody linked to a solid phase; reacting with second anti-human podocalyxin monoclonal antibody of which corresponding epitope is different from that of the first anti-human podocalyxin antibody; and measuring the second anti-human podocalyxin monoclonal antibody bound to the solid phase. The technique has problems that it cannot quantitate a trace amount of urinary podocalyxin, because the urine sample in almost neat concentration cannot be employed in the quantitation system; that accurate quantitative analysis of the urine sample cannot be carried out due to the deposition or accumulation of the inorganic salt precipitates derived from the urine sample, because the urine is not pretreated with the a chelating agent; and that the total podocalyxin content in the urine cannot be quantitated, because the solubilization with a surfactant is not carried out.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 6-011507
Patent Document 2 discloses a stabilizing preservative solution for urine αGST comprising a non-enzymatic protein in an amount enough for urine αGST stabilization, a chelating agent, and a buffer, thereby the reservative solution has the pH of 7.0 to 7.5, and is effective for preventing the loss of immunological activity of αGST. The technique has problems that accurate quantitative analysis cannot be carried out, because the urine pH is not completely compensated or homogenized; that accurate quantitative analysis cannot be carried out, because the precipitates of inorganic salts in the urine sample are not completely dissolved; and that membrane proteins present in the urine containing membrane components cannot be quantitated.
Patent Document 2: Published Japanese translation of PCT international application No. 10-507269
Patent Document 3 discloses a method for stabilizing urinary myoglobin and a preservative used in the method, the method comprising: adding to a urine sample a compound(s) selected from the group consisting of alkali metal azides, metal chelating agents, albumin, and saccharose. The technique has problems that accurate quantitative analysis cannot be carried out, because the urine pH is not completely compensated or homogenized; that accurate quantitative analysis cannot be achieved because the precipitates of inorganic salts in the urine sample are not completely dissolved; and that membrane proteins present in the urine containing membrane components cannot be quantitated.
Patent Document 3: Japanese Unexamined Patent Application Publication No. 10-282095
Patent Document 4 describes a method for stabilizing analytes in a urine sample, and a preservative for a urine sample using the method, the stabilizing method comprising: adding a urine sample a reducing oxygen acid salt and/or an isothiazolone compound, containing a buffer or an alkaline chemical, adjusting the pH value of the urine sample in the range of 6 to 9, and further containing a chelating agent. The technique has problems that accurate quantitative analysis cannot be carried out, because the urine pH is not completely compensated or homogenized; that accurate quantitative analysis cannot be achieved, because the precipitates of inorganic salts in the urine sample are not completely dissolved; and that membrane proteins present in the urine containing membrane components cannot be quantitated.
Patent Document 4: Japanese Unexamined Patent Application Publication No. 2000-352565
Patent Document 5 discloses an analytical reagent for analyzing formed elements in the urine, comprising a buffer for keeping the pH in the range of 5.0 to 9.0 and a chelating agent. The technique has the problems that the components of the urine supernatant or the whole urine cannot be quantitated, as it is an analytical reagent for analyzing formed elements in the urine, and that almost neat urine samples cannot be treated.
Patent Document 5: Japanese Unexamined Patent Application Publication No. 8-170960
Patent Document 6 describes that the urine sample is treated with a surfactant during the quantitation of urinary podocalyxin. The technique has problems that accurate quantitative analysis cannot be achieved because the urine pH is not completely compensated or homogenized; and that accurate quantitative analysis cannot be carried out because the precipitates of inorganic salts in the urine sample are not completely dissolved.
Patent Document 6: International Publication No. WO 2002/037099, brochure